The present invention relates to a method for printing on a spherical object to be printed such as a golf ball. Also, the present invention relates to a pad used for such a printing method, and a golf ball on which printing is performed by such a printing method.
As a device for printing images such as letters and pictures, a pad printing system has been used. The pad printing system has an elastic pad and operates as described below. On the surface of a printing plate, recesses are formed according to an image to be printed. Ink is applied onto the surface of the printing plate and fills the recesses. A pad is pressed against the surface of the printing plate, thereby transferring the ink in the recesses to the pad. Further, the pad is pressed against an object to be printed, by which the image is printed on the object to be printed. Since the pad has elasticity, the pad printing system can print images on not only a flat surface but also a curved surface such as a golf ball surface as described, for example, Japanese Patent Application Publication No. 2004-243033.
For the conventional pad printing system, there arises a problem as described below when an attempt is made to print the whole surface of a spherical object to be printed. In the case where the whole surface of the spherical object to be printed is printed, usually, the spherical object to be printed is replaced with a polyhedron at least a tetrahedron, and the pad is pressed against the faces a number of times according the number of faces. Therefore, in order to print the whole surface of a sphere, the pad must be pressed against the sphere many times at least four times, so that the productivity is low.
Also, in the case where a spherical surface is pad-printed, the photoengraving work is troublesome. For example, in the case where the spherical surface is printed using a pad having a substantially conical shape, the image formed on a plane-like printing plate is printed on the spherical surface in such a manner that the image distorts so as to extend long from the center toward the outside of the pad. Therefore, when the image to be printed on the spherical surface is formed on the plane-like printing plate, photoengraving must be performed by correcting the length of image and the depth of ink groove considering such distortion of image.
As the number of faces to be printed increases, the number of form plates to be manufactured increases. Therefore, the increase in printed face further imposes a burden on the photoengraving work. Also, it is necessary to transfer the image on each printing plate to the spherical surface of the object to be printed while aligning the mutual positions. Therefore, the increase in printed face also imposes a burden on the transferring work involving positioning work.